Charged particle multiplicity fluctuation in $A-A$ collisions at RHIC and LHC energies using Angantyr model

Abstract: Event-by-event fluctuations of the charged particle multiplicity are studied for a wide range of centralities for Au$-$Au collisions at $\sqrt{s_{NN}}$ = 200 GeV, Pb$-$Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV and 5.02 TeV using the Pythia 8 Angantyr model. The centrality dependence of $\omega_{ch}$ observable, which quantifies the fluctuations in terms of scaled variance is studied for different pseudorapidity ranges and has been compared with those obtained from a simple participant superposition model. The $\omega_{ch}$ was found to be lower than the expectations from the participant model. The estimate would act like a baseline for current and future measurements of event-by-event fluctuations in the charged particle multiplicities in systems at LHC energies where no de-confined medium of quarks and gluons are formed.